Lecture Notes: Gas Exchange in Terrestrial Insects

Overview

• Focus on gas exchange in terrestrial insects
• Anatomy, adaptations, and water loss prevention

Anatomy of Terrestrial Insects

• Exoskeleton
  • Made of chitin: hard, fibrous material for protection
  • Contains a lipid layer to prevent water loss
• Ventilation and Gas Exchange
  • No lungs
  • Tracheal system instead

Adaptations to Limit Water Loss

• Essential for survival on land (terrestrial environment)
• Key Adaptations:
  1. Small Surface Area to Volume Ratio
     • Limited water evaporation surface
  2. Lipid Layer
     • Makes the exoskeleton waterproof
  3. Spiracles
     • Tiny holes on the abdomen for gas exchange
     • Can open and close to control water loss

Tracheal System

• Components: Spiracles, Tracheae, Tracheoles
• Spiracles
  • Valve-like openings along the abdomen
  • Control water loss and gas entry/exit
• Tracheae
  • Network of internal tubes
  • Rings to strengthen and prevent collapse
• Tracheoles
  • Smaller tubules branching from tracheae
  • Deliver oxygen to respiring cells

Gas Movement in the Tracheal System

1. Simple Diffusion
   • Oxygen used up, carbon dioxide produced by respiring cells
   • Concentration gradient allows diffusion
2. Mass Transport
   • Muscle contractions in the abdomen move gases
   • Increases volume of gases exchanged
3. Fluid Pressure Changes
   • Occurs during flight
   • Switch to anaerobic respiration producing lactate
   • Lowers water potential, causing water movement
   • Decreases pressure and volume in tracheoles, drawing in air

Summary

• Large Surface Area: Numerous fine tracheoles and spiracles
• Short Diffusion Pathway: Thin tracheole walls, short distance between spiracles and tracheal system
• Maintaining Concentration Gradient: Respiring cells use oxygen, produce carbon dioxide
• Importance of maintaining a steep diffusion gradient for efficient gas exchange